A ratio of peak power to average power of a signal is referred to as “PAPR (Peak to Average Power Ratio)”. To improve the operating efficiency of a power amplifier in a transmitter, it is necessary to reduce a backoff in the power amplifier. For the reduction of the backoff, the PAPR of a transmission signal is preferably low. Accordingly, for example, when the transmission signal is a constant envelope signal having a constant amplitude, the PAPR of the transmission signal can be set to 0 dB because the signal power of the transmission signal is always constant.
Generally, the transmitter oversamples a signal, performs a band-limiting process on the oversampled signal, and then transmits the signal. Specifically, as described in Patent Literatures 1 and 2 or the like, V−1 zeros are inserted between samples of the signal, thereby multiplying a signal length by V (V-times oversampling). Thereafter, a band-limiting filter performs the band-limiting process on the oversampled signal. As the band-limiting filter, a root roll-off filter is often used.